1. Technical Field
The present invention relates to an ADPCM transcoder comprising
an encoder for a first conversion of a PCM signal originating from a PCM input into an ADPCM signal to be generated via an ADPCM output, and PA1 a decoder for a second conversion of an ADPCM signal originating from an ADPCM input into a PCM signal to be generated via a PCM output. PA1 delay means for delaying at least one of said conversions. PA1 at least one memory coupled to at least one of said coders for temporarily storing at least one signal originating from at least one of said inputs for avoiding overrun due to said delaying. PA1 a hardware unit comprising at least one of said coders and constructed from logic elements for performing arithmetic functions and logic operations without using instructions. PA1 use can be made of an existing clock signal DCL, which eliminates the need for an external quartz clock source. In addition, such an ADPCM transcoder has low power consumption, PA1 the ADPCM transcoder can be used for algorithms specified in Recommendations G.727/G.726, PA1 the ADPCM transcoder can be used for code conversion for the standards DECT, PWS and PHS, PA1 the ADPCM transcoder can be used for voice compression for voice servers, and PA1 a plurality of parallel ADPCM transcoders can be used for providing a pool of channels.
Such an ADPCM transcoder converts signals of different bit rates from one code to another.
2. Discussion of Related Art
ITU-T Recommendation G.727 specifies ADPCM (adaptive differential pulse code modulation) algorithms. The Recommendation defines the principles for transcoding a 64-kb/s PCM (pulse-code-modulated) signal into an ADPCM signal. According to the Recommendation, this can be a 40-, 32-, 24-, or 16-kb/s ADPCM signal (from: CCITT Recommendation G.727, General Aspects of Digital Transmission Systems; Terminal Equipments; 5-, 4-, 3- and 2-Bits Sample Embedded Adaptive Differential Pulse Code Modulation (ADPCM), Geneva, 1990).
Circuits for ADPCM transcoding include one or more processors. By means of such a transcoder, a plurality of channels must be transcoded. In DECT (Digital European Cordless Telephone), for example, 12 channels must be available. Conventional ADPCM transcoding circuits make available a maximum of four channels each. Thus, to make available 12 channels for DECT, for example, at least three transcoding circuits must be provided. This means that at least three different processors (DSPs) are required to make available 12 channels. This results in high power consumption and entails considerable costs.